Watershed Hydrologic Units for Alabama

(Taken from 11-digit Hydrologic Unit for Alabama abstract,
http://www.gsa.state.al.us/gsa/gsa.html

This data set is a digital hydrologic unit boundary that is at the
Watershed (11-digit) level for the State of Alabama. The data set was
developed by delineating the boundary lines on base maps and
digitizing the delineated lines. This data set consists of
geo-referenced digital map data and attribute data. The map data,
which were captured from 7 1/2 minute quadrangles, comprise a seamless
data layer for the entire State of Alabama. All land area within the
state can be characterized uniquely as being contained in one and only
one hydrologic unit boundary at the 11-digit level. The hydrologic
unit ID code attached to each delineated polygon is linked to the
attribute data.

The Watershed hydrologic unit boundaries provide a uniquely identified
and uniform method of subdividing large drainage areas. These smaller
sized hydrologic units (up to 250,000 acres) are useful in many
programs supported by federal and state agencies and others. These
data are appropriate for use in GIS applications.